Am I eligible for an upgrade to Elements 15?

I'm currently working with Photoshop Elements 4.0, and have been for about 10 years or so. I got it for free; I can't even remember exactly what it came with, but my grandfather had bought something and it came with a disk with a few free programs on it - and Photoshop Elements 4.0 was one of those programs. It has served me well for many years, but as of late, I have noticed a decline in functionality and would like to upgrade to a newer version.

So, I was on Adobe's website looking into buying Photoshop Elements 15, and I noticed that it is less expensive if you choose the Upgrade option (rather than buying it outright) so I'd like to take advantage of that deal, if I can. My question is whether or not it matters what version I currently have - and probably more importantly, how I got it. As I have described above, my circumstances are a little unique, so I don't know if that would disqualify me for the upgrade deal. I'm kind of assuming that it does, but I wanted to inquire first before going ahead and paying the full price.

TLDR;

• I have Adobe Photoshop Elements 4.0, which I'm pretty sure is more than 10 years old.

• I received it as part of a free software bundle, rather than purchasing it.

• Do either (or both) of these details disqualify me from buying the Upgrade version of Photoshop Elements 15?

I realize this is a long shot and I probably sound really stupid, but I just want to be completely sure.